1. Field of the Invention
The present invention relates to a substrate cleaning method for cleaning a surface of a substrate such as a semiconductor wafer, and more particularly to a substrate cleaning method for use in a substrate cleaning process for cleaning a surface of a substrate after polishing such as CMP. The substrate cleaning method of the present invention can be applied also in a cleaning process, e.g., in the production of a flat panel, a CMOS or CCD image sensor, or a magnetic film in an MRAM.
2. Description of the Related Art
In a damascene interconnect forming process for forming interconnects in a surface of a substrate by filling a metal into interconnect trenches formed in an insulating film in the surface of the substrate, for example, an extra metal on the surface of the substrate is polished away by chemical mechanical polishing (CMP) after the formation of damascene interconnects. A slurry (residual slurry), remaining after its use in CMP, metal polishing debris, etc. are present on the surface of the substrate after CMP. Therefore, such residues (particles), remaining on the surface of the substrate after CMP, need to be cleaned off. These days copper as an interconnect metal and a so-called low-k film having a low dielectric constant as an insulating film have come to be used in damascene interconnects. The hydrophobic properties of a low-k film leads to non-uniform wetting properties of a surface of a substrate after CMP, on which copper and a low-k film are exposed. This makes cleaning of such a surface of a substrate difficult.
As a cleaning method for cleaning a surface of a substrate after CMP, a roll scrub cleaning method is known which comprises scrubbing the surface of the substrate, such as semiconductor wafer, with a long cylindrical roll cleaning member (roll sponge or roll brush) by rotating the substrate and the roll cleaning member while keeping the roll cleaning member in contact with the surface of the substrate in the presence of a cleaning liquid.
In roll scrub cleaning of a surface of a substrate by a roll cleaning member, as the roll cleaning member becomes contaminated, the surface of the substrate can be contaminated by the contaminated cleaning member especially when the surface of the substrate is hydrophobic. A pencil scrub cleaning method is known to be effective for cleaning a surface of a substrate which has undergone such back contamination. In particular, a surface of a substrate after roll scrub cleaning is cleaned with a vertically-extending pencil-type cleaning member by rotating the substrate and the pencil-type cleaning member while keeping the surface of the substrate in contact with a lower surface of the pencil-type cleaning member in the presence of a cleaning liquid. Such pencil scrub cleaning can remove back contamination of the surface of the substrate from a roll cleaning member and can enhance the overall cleaning performance due to the integrated effect of roll scrub cleaning and pencil scrub cleaning.
FIG. 1 is a flow chart showing an exemplary cleaning process in which a surface of a substrate after polishing is successively cleaned by roll scrub cleaning and pencil scrub cleaning, followed by drying. First, roll scrub cleaning of a surface of a substrate after polishing is carried out by rubbing a rotating roll cleaning member against the surface of the substrate while horizontally rotating the substrate and supplying a cleaning liquid, which is an acidic liquid chemical, to the surface of the substrate. Thereafter, a rinsing liquid, such as pure water, is supplied to the surface of the substrate to rinse off the cleaning liquid (liquid chemical) remaining on the surface of the substrate. Next, pencil scrub cleaning of the surface of the substrate is carried out by rubbing a lower surface of a rotating pencil-type cleaning member against the surface of the substrate while horizontally rotating the substrate and supplying a cleaning liquid, which is an acidic liquid chemical, to the surface of the substrate. Thereafter, a rinsing liquid, such as pure water, is supplied to the surface of the substrate to rinse off the cleaning liquid (liquid chemical) remaining on the surface of the substrate. The substrate after cleaning is then dried, e.g., by spin-drying.
When a surface of a substrate is polished, recessed portions can be formed in the surface of the substrate due to dishing or erosion. It is generally difficult to remove particles, existing in such recessed potions, by scrub cleaning. Two-fluid jet (2FJ) cleaning using a two-fluid jet is known to be effective for removal of such particles. The two-fluid jet cleaning method is mainly employed for an interconnect metal which hardly corrodes by oxidation, such as tungsten, or in the production of an article in which corrosion of copper interconnects does not affect the product performance.
The two-fluid jet cleaning is a non-contact cleaning method which, unlike ultrasonic cleaning which is another non-contact cleaning method, is free from a fear of destruction of a substrate due to cavitation, and which is known to be effective for removal of particles, especially relatively large particles (e.g., having a particle diameter of more than 100 to 200 nm), adhering to a surface of a substrate with a relatively small adhesion force. When ultrapure water is used as a cleaning liquid, there is a fear of electrostatic destruction of a surface to be cleaned, e.g., a surface of an insulating film, because of the high resistivity of ultrapure water. Therefore, carbonated water, comprising pure water or ultrapure water containing dissolved CO2, is generally used as a cleaning liquid.
A substrate processing method with high cleaning performance has been proposed which cleans a surface of a substrate by successively carrying out scrub cleaning of the surface of the substrate with a cleaning brush and two-fluid jet cleaning of the surface of the substrate by the use of a two-fluid nozzle (see patent document 1). Further, the use of an alkaline cleaning liquid, e.g., in scrub cleaning has been proposed in order to prevent a lowering of the reliability of copper interconnects and a lowering of the product yield due to short circuit or open circuit of the interconnects (see patent document 2).
The applicant has proposed a substrate cleaning method with high cleaning performance which comprises carrying out scrub cleaning of a surface of a substrate, e.g. after polishing, with a roll cleaning member, and then carrying out two-fluid jet cleaning of the surface of the substrate using water (carbonated water) containing dissolved CO2 gas as a cleaning liquid, followed by drying the surface of the substrate (see patent document 3).
FIG. 2 is a flow chart showing an exemplary cleaning process in which a surface of a substrate after polishing is successively cleaned by roll scrub cleaning, pencil scrub cleaning and two-fluid jet cleaning, followed by drying. First, as in the above-described cleaning process shown in FIG. 1, roll scrub cleaning of a surface of a substrate after polishing is carried out with the use of an acidic liquid chemical, followed by rinsing the surface of the substrate to remove the cleaning liquid (liquid chemical) remaining on the surface of the substrate. Next, as in the above-described cleaning process, pencil scrub cleaning of the surface of the substrate is carried out with the use of an acidic liquid chemical, followed by rinsing of the surface of the substrate to remove the cleaning liquid (liquid chemical) remaining on the surface of the substrate. Next, non-contact two-fluid jet cleaning of the surface of the substrate is carried out by jetting a two-fluid jet flow, using acidic carbonated water as a cleaning liquid, toward the surface of the substrate, followed by rinsing the surface of the substrate to remove the cleaning liquid (carbonated water) remaining on the surface of the substrate. The substrate after the two-fluid jet cleaning is dried, e.g., by spin-drying.